The present invention relates to a propeller mechanism for a marine vehicle, providing the rotation of the propeller softly at a speed suitable to the current speed of the marine vehicle, in case the motor, the shaft and the propeller attached to it reduce speed or stop. The propeller mechanism of the invention also prevents both the transmission of reverse torque to the motor side and water resistance of the propeller during cruising of the marine vehicle.
The propulsion required for the movement of marine vehicles, such as boats, ships (including sailing boats) is provided by the propeller or propellers. Propellers, in general, comprises a central hub and a number of blades combined with the hub. The surfaces of the blades are generally in helicoidal form and water moving through the propeller is caught by the leading edge of the blade and compressed on the helicoidal surface to form a pressure and then it accelerates over the blade and leaves from the trailing edge to ensure the movement in progress.
The propeller is rotated by a shaft placed in a hole in the middle of the hub and connected to the motor and to its gearbox. As the propeller is directly and rigidly connected to the shaft, the rotation of the shaft in a direction causes the marine vehicle in the forward direction, and rotation of the shaft in the opposite direction causes the marine vehicle to move in the backward direction. The rigid character of the propeller shaft-propeller connection causes a sudden and sharp slow-down of the vessel if the motor is suddenly decelerated or stopped. In cases of a sudden halt from high speeds, depending on the current speed of the vessel, the negative acceleration is sometimes so great that the occupants of the vessel in the sea may feel discomfort due to reaction created. Furthermore, with rigid shaft-propeller connections, problems such as mechanical fatigue, wear may also be experienced as serious reaction forces will be created in case of stopping the motor and transmission.
As far as a sailing boat is concerned, when the motor is not running, water rotates the propeller by applying force on the blades of the propeller to create a reverse torque on the propeller shaft connected to the propeller and causes the rotation of the shaft according to the speed of the sailing boat. In this case, as the motor is not running, lubrication needed by the motor and transmission mechanism will not be possible and unless other remedy and measures are not taken, this can only cause a serious damage on the motor.
Numerous solutions to overcome this problem are proposed in the art, but none of them is economically feasible to be produced. In fact, according to a known solution for the sailboats, the propeller blades are displaced so as to split the water or folded back and the blades are brought back to their original position when the motor power is desired to be utilized. Another solution utilizes clutching valves (trolling valves) to be provided to transmission.
Yet further drawback applies to twin-motor boats. In particular, when one of the motors fails to run, the propeller at the side with the failure, may apply reverse torque to the motor side if no supplementary mechanism is provided for locking the corresponding shaft. This however would not prevent resistance created by the propeller fixed in the water.